The present invention relates to the treatment of industrial and/or urban waste and more specifically to the thermolysis thereof.
Several implementations have already been proposed in the field of thermal treatment of waste.
Thus, the applicant has presented in patent application FR-A-2,668,774 a process and a plant comprising a waste thermolysis operation, followed by a hot and dry treatment of the effluents resulting from the pyrolysis. The purpose of this implementation is essentially to reduce, or even to remove most of the pollutants present in the pyrolysis effluents, which are usually discharged into the atmosphere.
In the same field, document DE-35, 09,275 discloses a process for treating urban waste according to which this waste is successively dried, heated and then cooled, and the gases resulting from the combustion may be treated and thereafter partly discharged into the atmosphere and partly recycled.
As for the treatment of the solids resulting from the thermolysis, the applicant has also disclosed a thermolysis treatment of the waste comprising a dechlorination stage by washing said solids.
This implementation has notably the advantage of producing a coke cleared of the most part of the pollutants, that is to say a coke which is easily re-usable, having an improved calorific power in relation to systems which do not treat the solid products resulting from the thermolysis.
The object of the present invention is to improve the thermolysis of industrial waste by proposing not only to achieve a dechlorination of the solids resulting from the thermolysis, but also to directly heat the waste, through contacting in the pyrolysis means, with warm heat-carrying gases.
The present invention offers the following advantages in relation to an implementing without contact, through external heating:
the thermolysis means is simplified in relation to the devices using an indirect heating since the external heating means disappear;
tightness problems are considerably reduced since tightness is limited to inlets and outlets of reduced section;
the power consumption of the process according to the invention is lower than with an indirect heating, because, according to the present invention, the gases come out at relatively low temperatures and no longer at the final thermolysis temperature. Besides, for the same degree of insulation, the heat losses of the thermolysis means are much lower;
the size of the thermolysis reactor (or means) is reduced on account of the waste occupying almost the total volume available;
the yield of the coke having an improved calorific power is increased through an almost complete decomposition of the tars. In fact, the tars circulate partly in closed circuit, which means that the tars produced in the warm zone migrate towards the cold zone in the gas phase, condense in said cold zone, then go back to the warm zone, carried along by the solids, where they undergo a new cracking and so forth, so that they finally disappear almost completely to the advantage of the coke and the incondensable gaseous fractions.